Balancing means for rotating wing



Nov. 28, 1950 H. T. AVERY BALANCING MEANS FOR ROTATING WING 6Sheets-Sheet 1 Filed Feb. 4, 1946 a, r S v. WM W u: WT, m I, 10 MT 0. mT Rim a 0 ,w A W 7 B i I I I. N Q3 H. T. AVERY BALANCING MEANS FORROTATING WING Nqv. 28, 1950 6 Sheets-Sheet 2 Filed Feb. 4, 1946 KNVENTORW A T d l M m ATTORNEYS Nov. 28, 1950 H. T. AVERY BALANCING MEANS FORROTATING WING 6 Sheets-Sheet 5 Filed Feb. 4, 1946 5 RW Y O E E TV m mvfM M 0 mM H Y B Nov. 28, 1950 H; T. AVERY BALANCING MEANS FOR ROTATINGWING 6 Sheets-Sheet 4 Filed Feb. 4, 1946 \w w & Qw ww W N M \Q 0 Wk WA 7h mjuF n m Q M NR Y W 8 H 85m mm *N mm blw%jm$ Q 7 Q \wfi. H @J 2: m g:E Q Q Q R. MW mu mm WWW ATTODNEYS Nov. 28, 1950 H. T. AVERY 2,531,598

BALANCING MEANS FOR ROTATING WING Filed Feb. 4, 1946 6 Sheets-SheecfiFLLE 9 I INVENTQR HO/"O/Q Z A very V WM ATTORNE Y5 Nov. 28, 1950 H. 'r.AVERY 2,531,598

BALANCING MEANS FOR ROTATING WING Filed Feb. 4, 1946 6 Sheets-Sheet eFLE E INVENTOR HG/fO/Q T Avery WWW ATTORNEYS Patented Nov. 28, 1950UNITED STATES PATENT OFFICE BALANCING MEANS FOR ROTATING WING Harold T.Avery, Oakland, Calif.

Application February 4, 1946, Serial No. 645,309

12 Claims.

This invention relates to rotating wing aircraft and particularly toimprovements in the sustainin rotors for such craft. It is disclosed asapplied to rotors of the articulated type, that is, rotors in which theblades are hinged to a central hub member, and it is in rotors of thistype that the advantages of the invention may be most fully realized.

Rotors of both the articulated type and the non-articulated type areknown in the art and machines embodying each type have been constructedand flown. In rotors of the non-articulated type each blade of the rotoris free to be rocked on its own longitudinal axis to effect change inblade pitch, but except for such further slight changes in relationshipas may be introduced by the bending of the blades due to their ownflexibility it is otherwise fixed with respect to the rotor hub. Inrotors of the articulated type, the blades ordinarily retain the samefreedoms of movement relative to the hub as in rotors of thenon-articulated type plus: (1) the freedom provided by introducing aso-called flapping hinge at the root of each blade permitting the bladeto be fully rocked up and down in response to the forces acting on it inflight,

and usually also (2) the freedom provided by,

additionally introducing near the root of each blade a so-called draghinge permitting it to be angularly displaced in its general plane ordone of rotation.

Rotors of the articulated type exhibit a number of advantages ascompared to rotors of the non-articu1ated type, among which are thefollowing:

1. The stresses in the blades, and particularly at the blade root, areminimized.

2. Because of this, much less effort is required to effect the rockingof the blades on their own longitudinal axes to introduce changes ofpitch.

3. Since each blade is free to readjust itself in response to allchanges or disturbances in flight conditions, instead of transmittingsuch disturbances to the craft itself, the articulated rotor is the mostsuccessful in smoothing out air disturbances.

' 4. This same inherent ability ofthe articulated rotor to readjustitself to all kinds of flight conditions gives greater insurance againstits being forced into dangerous flight attitudes, hence providing arotor which is inherently safer under adverse flight conditions.

5'. If used in conjunction with a pitch control arrangement in which thepitch of each blade controlled through a link pivotally attached to itforward and outboard of its flapping hinge, the rocking of the bladeabout its flapping hinge can be arranged to provide inherent safetyagainst stalling of the rotor in case of engine failure, and to providesuch safety in the simplest and safest manner conceivable, for slowingdown of the rotor will automatically reduce blade pitch into the rangeof pitch settings capable of sustaining auto-rotation.

It is, therefore, not surprising that up to the present time allrotating wing aircraft (of both the Autogiro and helicopter types) whichhave been repetitively produced in any quantities and flown under anygreat variety of weather condi tions are sustained by rotors of thearticulated blade type. Such rotors, however, have certain disadvantagesas compared to rotors of the nonarticulated type. One of the chiefdisadvantages of the articulated rotor lies in the prevalence of largeamounts of vibration in that type of rotor.

I have observed that such vibration is primarily due to the manner inwhich the center of gravity of such rotors is continually shifting, sothat a rotor which is perfectly balanced un der one set of conditionswill be out of balance under other conditions. These shifts areprimarily due to unequal displacement of the respective blades abouttheir respective drag hinges and/or unequal rocking of the blades abouttheir respective flapping hinges.

One of the most troublesome sources of such the same circumstances, andhence cause that blade to continuously ride higher or lower than thetrack described by the other blades in their circuits. So long as allblades follow exactly the same track, and particularly if there are morethan two blades in the rotor, inequalities in the flapping angles of theblades at different points in the circuit do not tend to cause veryserious vibration,- for under these circumstances the center of gravityremains permanently displaced in a direction generally opposite to thatpart of the circuit in which the blades rock the highest, and the centerof gravity remains very nearly fixed relative to the craft. However, ifthe aerodynamic characteristics of one blade cause it to permanentlytrack any higher or lower than the others it will cause the center ofgravity of the rotor to be shifted away from or toward that blade in allparts of its circuit, thus producing substantially the same efiect as aneccentrically located weight rotating with the rotor, which of courseproduces bad vibration. Also, if the pitch setting of a blade with suchdifferent aerodynamic shape is readjusted. relative to that of the otherblades by an amount suflicient to bring it back into substantially thetrack described by the other blades its diiference in aerodynamic shapeis very apt to cause a difference in drag which will cause that blade tobe displaced differently from the others about its drag hinge, thuscausing a shift in the center of gravity of the rotor in' the directionof such dilference of displacement, which again is equivalent to aneccentric weight rotating with the rotor and causes objectionablevibration. A great deal of the trouble and expense involved in themanufacture and maintenance of articulated rotors is due to the effortto secure and maintain perfect aerodynamic simi arity, as well asperfect mass balance, between all blades.

A second shortcoming which, as a rule, is more 43. from each other inthe amount and distribution of mass in the respective blades.

It is an object of this invention to improve the degree of sensitivenessof the craft particularly in its pitching and rolling responses totilting of the rotor, and especially to provide the designmarked in thearticulated than the non-articue lated rotors as actually constructed isthe tendency for the blades to droop low enough as the rotor is beingstarted or stopped so that they constitute a menace to personnel in theimmediate vicinity of them. As soon as the blades attain anyconsiderable fraction of their normal rotational speed, they developenough lift to rock 'upward v about their flapping hinges at a coningangle sufficient to remove this menace. Because the blades of anarticulated rotor do not have to be constructed with sufficient strengthand rigidity to transmit bending moments to the central hub, andordinarily are not so constructed, they must be permitted to freely rockas low about their flapping hinges as there will ever be any tendencyfor them to rock in flight, which together with the lesser rigidity ofthe blad s ordinarily emploved in the articulated ro-' tor increases thetendency for this droon to reach such proportions in this type of craftas to invol e dan er to personnel or objects stand ing under the outerportion of the rotor when it is started or sto ped. Furthermore, thenonarticulated rotors have usual y been em loyed in double rotor craft,the two rotors usually being co-axial, while the articulated rotor hasusually been employed in a single rotor craft, thus as a rule requiringthe use of a greater rotor di ameter. and conseouentl greater droon.

A primary object of the present invention is to provide an improvedsustaining rotor for rotating wing aircraft.

A further primary object of the invention is to remove the necessity foraerodynamic similarity between the various blades of a rotor,

which has been an indispensable and costly necessity in articulatedblade rotors, and thus to provide a rotor which will be easy andinexpensive to manufacture and maintain.

A further primary object of the invention is to substantially reduce orcompletely eliminate .the vibration which has heretofore beencharacteris'tic particularl of the articulated rotor.

More specifically, it is an object to provide a rotor which will possessall the advantages of the articulated rotor, as above outlined, but noneof the disadvantages thereof, as above described.

It is also an object of the invention to provide novel means for easilybalancing a rotor even though the blades of the rotor difierconsiderably ers of such craft with novel means for decreasing orincreasing such sensitiveness as desired.

It is also an object of this invention to avoid the droop of the rotorblades which has heretofore been characteristic of the blades when therotor is stopped or turning slowly.

' The novel features of the invention are set forth with particularityin the appended claims. The invention itself, however, together withadditional objects and advantages thereof will be best understood fromthe following description thereof, when the same is read in connectionwith the accompanying drawings, in which:

Figure 1 is a diagram illustrating, in accordance with the practices ofdescriptive geometry projection, certain of the movements of the blades,and particularly of the centers of gravity thereof, in articulatedsustaining rotors characteristic of the prior art.

Figure 2 is a similar diagram of a rotor embodying my invention.

Figure 3 is a diagram illustrating in elevation the eifect of rotor tilton resultant lifting and other controlling forces in rotors of the priorart and those involving my invention.

Figure 4 is a diagram illustrating in elevation the flapping movement ofa blade and showing dimensionally the operation of the novel means Iemploy for stabilizing the center of gravity of the rotor andeliminating cyclic accelerations and decelerations of the blades.

Figure 5 is a plan view showing a rotor hub and the adjacent portion ofone of the blades embodying m invention.

Figure 6 is a partial vertical section of a rotor embodying myinvention, showing particularly in section a portion of one of theblades standing in its horizontal position and correspondinglypositioning certain of the novel mechanisms with which each of theblades is equipped.

Figure 7 is a view similar to Figure 6 but showing the blade rockedupwardly about its flapping hinge, and the related mechanismscorrespondingly displaced.

Figure 8 is a transverse cross-section of a blade embodying myinvention.

Figure 9 illustrates in section a yieldable' link shown in Figure 5.

Figure 10 is an enlarged sectional view of certain connecting andadjusting mechanisms taken substantiall on line XX of Figure 6.

Figure 11 is an enlarged view of a portion of Figure 6 showing thepiston mechanism in crosssection, and showing particularly the sub-unitsof which the piston and cylinder assemblies are constituted.

Figure 12 illustrates an alternative embodi ment of the invention, andals illustrates details of the mechanism pitch.

Referring to Figure 1 diagrammatically illus trating certain elementstypical of prior art construction embodying articulated rotors, thediagram is drawn in accordance with the practice of descriptivegeometry, wherein the mechanism is shown as projected onto twoco-ordinate planes rotated into the plane of the paper. The line XY isthe base line constituting the line of intersection of the twoco-ordinate planes.

for controlling blade 7 accuses:

The portion oil the drawing above the line: constitutes the projectionor the mechanism onto a vertical plane, and the portionbelow it theprojection of the same mechanism onto a horizontal-plane.'li'l'le'=.finedotted vertical lines are fol the purpose: of connectingone projection of each of certain: points to the other projectionthereon. so as to make the relationships discussed more readilyapparent.

The weight lifted by the rotor, which ordinan-1y oi the fuselage and itscontents, isdiagrammatically illustrated in Figure 1 as a sphericalweight [5, suspended from the-rotor hub f6. Pivotally attached to thishub by means of flapping hinges 24 are a plurality of blades ll,illustrated as two in. number in the. diagram, The center of gravity ofeach or these blades is located at a point t-8 -fi.xed in thebladc. Whenthe craft is hovering stationary in the air each blade l'l'xextendsoutwardly and. upwardly from the hinge which attaches it to hub 16 atsuch an' a-ngle that the vertical projection of the blade bears to itshorizontal projection the same ratiothatthe not hit contributed bytheblade bears to the centrlifugal force acting on the blade, and the:surn 'of the lift forces contributed by all blades equals the weight orthe craft Normally under 1 these "circumstances the axis is about. whichthe bladesare rotating extends vertically upward: and it the blades areaccurately similar they: maize equal angles with: the-"axis, and-theircenters of gravity l8 move in a truly horizontal circle 20:, and foruniform speed of the driving meansmove at uniforxmspeedi around thiscircle. A rotatiorrot one quarter turn, for-instance, fromtheip'ositions at which the blades are illustrated in. solid lines willbring their centers of gravity white the two diametrically oppositepositions [811, and if the axis of hub l6 coincides substantially withvertical axis 19, the angular movementof the hub will equal the angularmove ment of the bladeand n0 necessity will exist for any displacementof the blades about their drag hinges; a drag hinge as previouslymentioned being a hinge (usually substantially vertical and located nearthe root of a blade) for permitting the blade to be advanced or retardedrelative to the hub in its rotation.

[In order to impart horizontal movement to a craft which is sustained ina hovering position by an articulated rotor, as above described, it isnecessary to tilt the rotor in the direction of desired movement. Forinstance to produce rightward acceleration of the craft the rotor wouldbe tilted rightward into a position suchas that indicated by dottedlines in Figure 1, wherein the leftward blade I! is rocked upwardthrough the angle F into the position Ill), and the opposite bladerocked downward-by substantially the same angle to the position l is,bringing the centersor gravity 18 of these two blades to the positions18b and [80, respectively. Under these conditions the centers of gravityl8 rotate in the cirole 20b, concentrically located with respect to theaxis 196 which is tilted rightward by the tilt angle T from the originalaxis of rotationl9, the tilt angle T being nearly the same as the comcsponding angle F of blade displacement about flapping hinge,particularl if the diameter of hub I6 is quite small as compared withblade length. The resultant rotor force on the craft, now being directeddiagonally upward toward the right, has a horizontal component whichproduces horizontal rightward acceleration of the craft, which in turnproduces an opposing 6* drag forceon. the fuselage I5; The horizontalcomponent of the rotor force" being vertically 011- set from the: dragforce on; the: fuselage causes the craft to tilt; If the axis [19b ofrotor rotation be: maintained a constant angl to the vertical (notaconstant tilt relative to the craft), then as the horizontal speed orthe craft becomes greater and: consequently the drag force increases thetilt of the craft will increase while the net horizontal force producingacceleration will decrease, until finally the tilt of the craft equalsthe tilt of the rotor and the craft settles down to a uniform. speed orhorizontal movement with the rotor maintaining substantially its oriinal normal relationship to the but not to the vertical However; duringthe; time that any control is being exercised on the craft to produceany horizontal accelerations or deceleration thereof the rotor must betilted out of its normalrelati'onslrrip to the craft, and the conditionswhich. exist during this period of time will now be further analyzed.

In rotating: wing craft sustained by articulate rotors di'fl'erentmethods have been employed to effect the tilting of the: rotor relativeto the craft; In Autogiros it has hem customary to construct the bladesso that they will; maintain fixed Ditch angles relative tothen-respective flapping hinges during flight, "and toexercisehorizontalicontrol by tilting the rotor hub, which. tiltingangularly displaces the flapping hingesand consequently roduces changesin the pitch angles of the blades such as to produce aerodynamic forceswhich serve to so alter the path of movement of the blades as to bringthem into substantially the same positions relative to the tilted hubthat they originall held relative to the hub in its original osition.

In helicopters, however; suchtilting of the hub ordinarily involvesgreater mechanical complications on account of the continuous powerdrive connection from the engine to the rotor. Also in helicopters it ispossible to take advantage of the fact that it is ordinarily necessaryin such a craft to provide means for independently adjusting the pitchof the blades by individually rotating them ontheir own longitudinalaxes in order to exercise control for vertical climb and descent. All ofthis has resulted in a diiierent construction ordinarily being employedin articulated rotor helicopters, namely one in which the hub ismaintained on an axis fixed relative to the craft but in which the pathof blade movement may be altered by changes of blade pitch cyclicallimposed upon the blades so as to bring about a tilting of the cone ofblade movement very closely comparable to that produced by tilting ofthe hub in an Autogiro.

Although the invention is applicable to craft embodying either of thesearrangements, the following discussion of prior art construction, aswell as that relating to the invention, applies particularly to thearrangement wherein the rotor hub is maintained on an axis fix-edrelative to the craft, and tilting of the rotor is brought about bychanging the path of movement of the blades relative to the'hub throughcyclic changes of blade pitch. A typical rior art arrangement foraccomplishing this is illustrated and described in the magazine Aviationfor June 1945 at pages 122 to 13c, and there is referred to as theM74272 helicop 1'.

solid line positions of the blades.

7. line l9, then if the blades'are, as previously described, caused tomove in paths concentrically located relative to axis 191), each bladewill rock upward about its flapping hinge as it passes from position Heto position llb and downward as it passes from position ill) to positionHe. Also if the blades and the hub are to move with uniform rotationalspeed considerable displacement on the drag hinges will also beinvolved.

For instance when the blades occupy the position identified as 11b andHe in the upper projection of Figure 1, their horizontal projections arecolinear with the solid line positions labeled I1, I? in the lowerprojection, and the hub position is identical with that corresponding tothe If the hub is then rotated one quarter turn counter-clockwise fromthis position without any displacement of the blades about their draghinges, the projections of the blades will then be coincident with thevertical center-line IS in the upper projection and coincident with theextension of this line in the lower projection. The center of gravity ofthe right hand blade will have moved from point |8c to the point wherethe circle b crosses the center line H! (which point is very nearlycoincident with the upper point Illa in the lower projection and withthe point [8a in the upper projection), and the center of gravity of theleft hand blade will have moved from point l8b to the point where circle20b crosses back across the center line l9 (which point is very nearlycoincident with the lower point [8a in the lower projection, and in theupper projection is coincident with the point to which center of gravityI80 has moved as above described). 'It is obvious that under suchcircumstances the center of gravity l8c of the right hand blade hastravelled much further than the center of gravity I81) 01' the left handblade. In order for the centers of gravity [8b and Me to travel equaldistances from their original positions it would be necessary to havecenter l8c travel only to point l8d, which point is so located that itsvertical projection lies on the same line as the projection of axis [9b.Similarly center l8b must travel on to point We, the vertical projectionof which coincides with that of point l8d. In order to bring the centersof gravity of the two blades to positions l8d and l8e, one blade must bedisplaced clockwise through the angle D about its drag hinge, bringingthe horizontal projection of that blade to I 1d, while the other bladeis rocked counter-clockwise through the same angle about its drag hinge,bringing the horizontal projection of that blade to I la. The verticalprojection of both blades coincides with that of axis I in the case ofno displacement about the drag hinges, and coincides with that of axis[9b in case both blades are displaced in opposite directions through theangles D about their drag hinges as above described. Thus it is evidentthat it, with the rotor tilted to the right into is dotted lineposition, both the hub and the blades are to rotate at uniform speeds(which is necessary in order to avoid vibration of the craft due toaccelerations and decelerations of the blades or of the rotor drivingsystem) each blade must follow a pattern of movement in which (1) it isdisplaced in a lagging direction as its center of gravity movescounter-clockwise from point l8c until by the time it reaches point l8dthis lagging displacement about the drag hinge equals angle D; (2)thereafter it starts to advance about its drag hinge until as the centerof gravity reaches point 18b it is back again in its normal angularposition on its drag hinge; (3) it continues to advance until by thetime the center of gravity reaches point We the blade has advanced bythe angle D ahead of its normal position on its drag hinge; and l)thereafter it starts lagging again until upon return to point l theblade is again back in its normal position on its. drag hinge.

This same pattern of blade displacement is also necessary in order toavoid vibratory dis-- placements of the center of gravity of the entirerotor. The center of gravity of the entire blade system of the rotornaturally lies at the center of the circle described by the centers ofgravity of the blades providing these centers of gravity are alwayslocated in diametrically opposite directions from this center. When thero-' tor is in hovering condition, as indicated by solid lines, thecenter of gravity of the rotor lies at point 2|, the center of circle20. However, when the rotor is tilted as illustrated this center isdisplaced to 2| b, the center of circle 28b. That is,- it is evidentthat when the centers of gravity of the two blades lie at 812 and I80,respectively, the resultant center of gravity will be at 21b. Similarly,after the hub has rotated one quarter turn it is evident that the centerof gravity of the rotor will still lie at 211) providing the centers ofgravity of the blades lie at I 8d and Ne, respectively, but if nodisplacement of the blades about their drag hinges had been permitted totake place the projection of both blades wouldcoincide with center linel9 and the centerof gravity of the rotor would fall in a position bothprojections of which would fall on this center line, namely a positionvery nearly coinciding with the original location 2| of the rotor centerof gravity.'- Hence, if no displacement of the blades about their draghinges were permitted the center of gravity of the rotor would vibratetwice each cycle between point Zlb and a point substantially coincidentwith point 2|, which vibration would cause objectionable vibration ofthe craft. However, if the blades are displaced about their drag hingesso that when the center" of gravity of one blade lies at l Bd that ofthe other blades lies at I8e, not only do we attain uniform rotationalvelocity of the blades concurrently with uniform rotational velocity ofthe hub, as

previously described, but we also maintain the" center of gravity of therotor steadily at point 2 lb instead of causing it to vibratecyclically.

The foregoing description makes it clear why it has proved necessary toequip the articulated rotors'of the prior art with drag hingesindividual to the respective blades. However, these prior art rotorshave not been. equipped with any positive means to constrain the bladesto move in the desired manner about their drag hinges. By locatin thedrag hinges outboard of the rotational axis, centrifugal force on theblades has been made effective to yieldably resist displacement of theblades about their drag hinges, and other means have been sometimesutilized to supplement it in so doing. However, the momentum of theblades is principally responsible for producing the proper displacementsabout the drag hinges and if it is opposed by any of these other meansin so doing the resulting displace ment is less than the proper one andvibration results. This has been generally true of the articulated bladehelicopter of the prior art. Also irregular disturbances of the air maycause irregular displacement of the bladesabout their are-w drag hinges"with'consequent displacement .of the center of gravity of the rotor andcorrespond: ing vibration. When the craft is in close proximity to theground a particularly aggravated form of this condition may develop,wherein an air disturbance set up by one iblade may be rehosted from theground in such a path as to .di'r rectly engage another blade at cyclicintervals dependent upon rotor speed and craft movement. When theseintervals coincide with the natural frequency of blade displacement, acondition may result known as =ground resonance which may cause verydestructive vibration.

While the means, previously mentioned, for yieldably resistingdisplacement .of the blades is usually of a form" that will tend toreturn tonermal a blade that has been irregularly displaced, suchcentering action cannot be made very strong incomparison with the efiectof blade momentum indisplacing the blade about its drag hinge, or aspreviously mentioned the momentum will normally produce too small afraction of the proper displacement to suitably minimize vibration.Il'ierefore, the arrangement must be such that blade momentum is thepredominant factor in determinin the position of the blade about itsdrag hinge. But if this is the case the increment of-momentum impartedto the blade by an irregular displacement, such as above mentioned, willtend to cause the displacement to continue to increase after the airdisturbance originating the irregular displacement has disappearedandhence the irregular displacement caused by a small disturbance may reachconsiderable proportions and be very slow in disappearing, and

as lqng as it persists will causea displacement of rotor center of sucha nature that the displacement will rotate with the rotor and thereiorecause vibrations corresponding to those produced by an eccentricallyplaced weight. Hence, while it'has been necessary to provide drag hingesin the articulated rotors of the prior art, no means have been devisedto positively constrain the bladesto move properly about their draghinges, and such means as have been provided to produce the properdisplacements and ;to resist and wipe out the improper displacementshave conflicted with each other to a degree which has caused vibrationdue both to too greatly resisting the proper displacements and to notsufficiently resisting and correcting the improper displacements. Thatis, means must be provided to resist, at least yieldably,;improperdisplacements of the blades about their drag hinges, or such dis,-placernents will get completely ,outof hand and re se dest u e br t en-T Q W KJ W2 E g- 1 A a b n P Ovided f 12 .5 P '.P9 ,1 to ts inab i to dsc e b n rope nd i p d s ac men has e i t d th prope d s la em n of hblades u a mu as 'it has the improper displacements thereof. .Since lu abad vibration il b cau ed by ie hosit on o a bla ab t d a .h ese due toits proper displacements having been rehied as b h e am u t o mis ositimn due to the introduction of improper displace grants from extraneoussources the prior art me ns wh 1s a d s c ments have bee e apa o e miing v b e ien- Ea c the prio e timean o re sti g ras is lae meats-has neessa be i v Na u e a omprom s i qun t P odu cons dera l bret on by re sing the p nedisplac ems h heab ades i r istance to d s sal was greatenough to reasonably control the proper displacements .thereof..

The primary objects of my invention are at-' tained by the provision, ina bladed rotor, of a balancing weight adjustable radially with respectto the axis of rotation of the rotor and ofdevices actuated by blademovements tending to displace the center of gravity of the rotor fordirectionally and quantitatively adjusting the balancing weight so as tosubstantially prevent any displacement the center of gravity of therotor as a whole.-

The general manner in which this arrangement is erfectiveto attain theprimary objects; of my invention in the case of an articulated rotorwill be understood upon reference to Figure 2 of the drawing which isa-descriptive geometry projeotion of a rotating wing craft embodying myinvention. As in Figure 1 the fuselage and its contents, diagrammatic-ahillustrated by weight 15, is supported by a rotor comprising hub 46 andblades H, the latter having centers of gravity I 8, which when the rotoris tilted by bringing the blades to positions Nb and We, respectively,assume the positions lib and We respectively.

In order to eliminate the necessity for drag hinges individual to therespective blades, and at the same time eliminate the vibration characteristic of craft embodying such hinges, I provide in conjunction witheach blade a balancing weight 25 which is arranged to be automaticallyadjusted longitudinally with respect to its blade in accordance with theflapping angle of said blade in such a manner as to substantiallydisplacement of the resultant center of gravity of the entire -rotor.-

In the embodiment of the invention disclosed herein, these weights aremounted within the blades so that when the blades H are in their normalpositions, as shown b solid lines, these weights will occupy thepositions labe1led25 in Figure 2, under which conditions they move inthe horizontal circle 26 as the rotor rotates. l f now, in the mannerpreviously indicated the left hand blade is rocked upwardly on itsflapping hinge 24 to the position lib, thereby displacing the'center ofgravity of the blade itself from t8 to 181), means responsive to thischange of flapping angle automatically moves the correcting weight whichis incorporated in the blade from position 25 to 2519. The relativeweight of the blade and of the weight 25 are such that when the centerof gravity .of the blade lies at point vl-8 and that of weight 25 at thepoint iabelied 26; the resultant center of gravity of the combined bladeand weight is located at point 2d, and the amount of shift of the weightto position 256 when the blade is rocked up is such as to bring theresultant center of gravity .of the blade and weight in their raisedpositions to the point labelled z lb which is located directly abovepoint 2?! and hence the same distance from rotor axis- I9v Similarlywhen the right hand blade is rockeddown .to the position He, causingcenter of gravity to move further away from axis 19 to the position Iits weight 2.5 is .causedto shift inwardly to the position ilac-so esltoiihiiine theresultant center ,of gravity of the right hand 11 doesnot'alter or in any way disturb the center of gravity of the rotor, andthe center of gravity remains at all times on axis l9 at substantiallythe point 2|. Hence when the rotor is turned through one quarter turnfrom the position illustrated, the blades should occupy a position whichwill continue to retain the rotor center of gravity on axis i9 ifvibratory displacements are to be avoided, which means that allprojections of the blades should coincide with center line [9 of Figure2, as indicated at IT and Hg in the drawing, which is the conditioncorresponding to no displacement of the blades about their drag hinges.Since this condition applies for all possible flapping angles of theblades, drag hinges individual to the blades may be eliminated. Thiselimination will leave the blades always diametrically opposite eachother, thus entirely avoiding the shifts in rotor center of gravitywhich have heretofore been incident to irregular displacement of theblades about their drag hinges.

Heretofore it has been necessary to provide the drag hinges for reasonspreviously described and the pattern of movement which the blades mustdescribe about their drag hinges in order to preserve smooth operationwere of such a nature and so diflicult to predict that it was notfeasible to provide any mechanism capable of constraining the blades tofollow such a pattern of movement. Much of the trouble with vibration inarticulated rotors has been traceable to departure of the blades fromsuch a pattern of movement. However, by introducing in each blade such aweight automatically adjusted in accordance with the flapping of theblade in the manner described, the pattern of movement of the bladesabout their drag hinges required to preserve smooth operation is reducedto zero movement, and it becomes practicable to provide means toconstrain the blades to follow this pattern of movement, for all that isnecessary in order to do so is to eliminate the drag hinges individualto the respective blades, as heretofore necessarily provided.

As I shall later describe in more detail, I consider it desirable toprovide what amounts to a single master drag hinge common to all theblades, to permit some lagging or leading displacement of all blades inunison relative to the rotor driving mechanism in order to preventtransmission to the blades of any sharp irregularities in drive, and topermit them to respond to irregular air disturbances without, however,disturbing their horizontal angular relationship to each other nordisturbing the center of gravity of the rotor.

' As previously indicated, elimination'of the individual drag hinges inthe prior art structures would not only cause bad vibratorydisplacements of the rotor center of gravity but would also cause cyclicaccelerations and decelerations of the blades in a manner which wouldset up vibration'. It will therefore be in order to investigate theblade accelerations and decelerations with my new arrangements.

' With the rotor in its tilted condition, as indicated by the dottedline positions of the blades in the upper projection of Figure 2, thecenters of gravity l8 of the blades proper will movein essentially thesame eccentric path 20b (lower projection) as previously described inconnection with the prior art (Figure 1) and the mass centered at I8will be decelerated as it move from I80 through I81 to I81; andaccelerated as it moves on through l8g to I again. However thecounter-balancing weight 25, which under hovering conditions (with'theblades at the flapping angles indicated in solid lines) moved in theconcentric circle 26, alters its path of movement when the blades aredisplaced to their dotted line positions and moves in the eccentric path261), the eccentricity of which is opposite to that of path 281). Theweight 25 will be accelerated as it passes from position 250 through 25fto 25b and decelerated as it passes on through 25g to 250 again. Hencethe accelerations and decelerations of weight 25 will always be oppositeto those of the blade proper, and since the Weight is sup ported in theblade for movement parallel to the longitudinal axis of the blade thenet effect will be for these accelerations and decelerations to acttoward neutralizing each other. 7

While the mass of the weight 25 will ordinarily be much less than thatof the blade the amount of eccentricity of its path of movement willnecessarily be correspondingly greater than that of the blade proper inorder to maintain the resultant center of gravity of the weight andblade at a constant distance from the rotor axis, as previouslydescribed. In fact with the eccentricity of the path of movement of theweight such as to attain this objective, the accelerations anddecelerations of each blade and its related weight exactly neutralizeeach other. This is necessarily true because the net accelerating ordecelerating effect, if any, will be that of the resultant center ofgravity of the blade and Weight which, remaining at a constant distancefrom the axis, moves in the path 28b which lies in the same cylindricalsurface concentrically located with respect to axis I9 as does thecircular path 28 described by the resultant centers of gravity 2'! ofthe blades under balanced hovering conditions. The horizontalprojections of the path of movement of the resultant centers of gravity2'! is the identical circle 28, regardless of the flapping an+ gles ofthe blades, and therefore the rotational component of velocity of thesecenters of gravity :7 will always be constant and no net angularaccelerations or decelerations will be encountered.

Therefore, providing in conjunction with each blade a weight 25 andmeans for automatically adjusting it in the manner described, serves notonly to prevent the displacements of rotor center of gravity heretoforecaused by difierences in the flapping angles of the blades, but alsoeliminates the necessity for drag hinges individual to the blades,renders it feasible to automatically retain the blades at all times intheir proper horizontal angular relationship to each other, andeliminates the angular accelerations and decelerations of the bladeswhich have heretofore existed and which would become of prohibitiveproportions were the individual drag hinges eliminated without theincorporation of the automatically counterbalancing weight. a I

The manner in which the tilting of the rotor produces respondingmovements of the craft, is affected by the introduction of theautomatically adjusted weights into the blades. On the craft of theprior art, in which each blade is attached to the hub by a drag hingeand a flapping hinge about both of which it is freely displaceable, theblade cannot exert any continuing force on the craft except a tension inthe direction of the blade axis. Under ideal hoverin conditions allblades are rotating about a vertical axis at a constant flapping angle.In Figure 3 the solid lines I! represent two such blades. Under thesecon-I the'craft, as indicated by vector R1 in Figure '3.

If now the rotor be tilted rightward by rocking the left blade up toposition lib and the right blade down to position He, the rightwardhorizontal component of the aerodynamic force on the left blade willexceed the leftward horizontal component of theaerodynamic force on theright "blade. The resulting net rightward horizontal component of theaerodynamic forces on the two blades combined with their resultantupward component, causes the resultant force which the blades exert onthe craft to be angled upward toward the right, as indicated by vectorR2 (Figure 3). Also, if the two flapping hinges 24 are separated fromeach other, as illustrated, the raising of the left blade and loweringof the right causes the intersection of the axes of the two blades toshift leftward, the line of action of vector R2 passing throughthis newintersection.

If the amount of tilt of the prior art rotor :be increased by raisingtheleft blade to position ll'm (Figure 3) and lowering'the right blade toposition 7! in, both the angularity of the resultant "force and theoffset of its line of action from rotor center are increased insubstantially equal proportion, with the result that the new resultantforce exerted on the craft by the blades, as represented by vector R3,intersects the center line of the craft at approximately the same point132' at which vector R2 intersected it, which point is located above therotor. Therefore the tilting of the rotor displaces the line of actionof the aresultantrotor forces much further from the center of gravity l5of the sustained craft than they are displaced in the plane of therotor, meaning that "the turning moments tending to rotate the 'cra'ftare relatively large in comparison with the horizontal translationalforces brought into play "by the tilting of the rotor.

As will be later described in more detail the :n'leans which I employ toautomatically position the previously described weights 25 in the bladesin accordance with the flapping angles of the blades continually exertan upward moment on ll1'l6b13d about its flapping hinge, consequentlycausing the blade to exert an opposite moment on the craft as indicatedby the arrows M1 and'Mz inrFigure 3. The arrangement is such that themoment increases with increased flapping angle :of the blade at ratesslightly greater thanproapo'rtional to the increase in flapping angle.This therefore constitutes what is known as an unstable moment, since adisplacement of the blade relative tothe hub causes the moment to changein thedirection tending to produce further'such displacement. Nounstable condition of the blades-actually results, however, since themechfor producing moments M1 and M2 is-so arranged that these momentscan only act when centrifugal forces are acting on the blades, underwhich circumstances the moments exerted onthe blades by such centrifugalforces oppose the moments M1 and M2 and stabilize the. blades.

Under hovering conditions the moments M1 and M2 balance and theresultant blade forceon "the craft coincides with the rotor axisas'represented by vector R1 justas in the prior iartcraft.

lies below the motor. "of moments M1 and M2 with flapping angle, with mymechanism as disclosed, issuch that regardless ofrotortilt the resultantforce intersects the irotor axis at app-roximatelythe same point 33,

'ISpeCtlVe vectors R2 and R3. varying different factors-suchas thedistance of the weights "25 from the rotor axis and the distance of theflapping hinge from the rotor forces without tilting forces. meriteliminates substantially the last vestige nowever, if in my "craft therotor is tilted rocking the left blade to position Ho :and the right"blade to position He, the resultant .force exerted on the :craftbythelblades is tilted toiapproximately the same angle as in the prior artcraft, but the counterclockwise moment M1, ex-

'ceeding'theclockwise moment 1M2, leaves a net counterclockwise momentexerted on the craft, which combined with the resultant force (whichexcept for this unbalancedmoment would lie 'substantially along the lineof actionof vectorRz) iproducesthe ne'wiresultantrforce S2 which is off-:set from the force R2 of the prior art toward'the blade oflowerfiappingangle. This'force intersects the vertical axis of the rotor atpoint 33 The :rates of 'change the additionaltilt of the rotor to theextent represented'by blade positions l'lm and ll'nbringing theresultant blade force on the craft to the line of action indicated byvector S3, due'to'the tunstable pattern of variationsof moments M1 andM2.

- -Itwi1l b'e noted that the lines of action of vectors S2 and S3 passless than half as farfrom center of gravity l5 as the corresponding re-By appropriately axis the point33 may be established at any chosenlocation within a wide range. If point 33 were established at or nearcenter of gravity 1 5 (which ;falls well within the range of possiblelocations) tilting of the rotor will upro'ducetranslational Such anarrangeof vibrational'eifect from the rotor, for as previously describedmy proposed arrangement would eliminate all the various prior artsources of disturbances due to the various types of shiftling of centerof gravity and to rotational accelerations and decelerations.

However, a blade tracking continuously higher -orlower than its mates,due to aerodynamic dissimilarity would cause a displacement of theresultant rotor force similar to that caused by tilting of the rotorexcept that when the displacement is due to such dissimilar tracking theresulting force will rotate with the rotor rather than. remainingsubstantially fixed indirection.

If slight rotor tilts produce large turning ,mo-

ments on the craft, as with forces R2 and R3 of the'prior art (Figure 3)relatively smalldisturbances can set up considerable vibration due tothe rapidity with which rotational moments angularly displace the craft,butif the lift force always passes through the center of gravity,'such adisplaced blade will not produce any net "mo- ,ments-on the craft,although approximately the same translational forces are cyclicallyexerted as that associated with the same aerodynamic disturbances intheprior art, but these forces are so small, and the craft is relativelyso slow in responding to translational forces, that the eifect 'issubstantially negligible.

If the point 33 is located coincident with cenzontal force component onthe craft as previously Willexert less of a pitching or rolling moment,so that pitching and rolling effects of rotor disturbances andirregularities will be correspondingly minimized;

It has been characteristic of articulated blade helicopters in the pastthat they have been so sensitive to displacements of their pitching androlling controls that displacements of these controls, less in amountthan the vibrational displacements imparted to these controls by therotor, would produce marked responses of the craft. My invention makespossible to not only completely eliminate the chief sources of suchvibration in the prior art but to so arrange it that the craft will beslightly less sensitive in its pitching and rolling responses, althoughremaining substantially unchanged in translational response to itspitching and rolling controls. All of this makes for smoother and moredependable operation.

It is to be understood that while the foregogoing description, relatingto Figures 1, 2, and 3, has referred to two opposite blades and to rightand left directions, movements and forces, the same general effects andresults as outlined apply to a rotor equipped with three blades, fourblades, or any other number of blades, and the directions referred to asright and left might equally well constitute forward and back directionsrelative to the craft or any opposite directions in which it may bedesired to investigate or exercise the control.

The amount by which the flapping movement of a blade displaces itsrelated weight has thus far been defined only in terms of the results tobe attained, namely that the displacement is to be such as to maintainthe resultant center of gravity of the blade and weight at a constantdistance from rotor axis $9. With the aid of Figure 4 we may now expressthe position that weight 25 should occupy at any given flapping positionof the blade in terms of the blade flapping angle and the relativedimensions and weights of the parts involved. For this purpose:

Let

The distance of the resultant center of gravity 21h of the horizontalblade and its weight from the rotor axis as may be determined by takingthe moments of the blade mass and weight mass 1'6 about the axis anddividing by the combined mass:

, The distance of the resultant center of gravity 2? of the bladestanding at flapping angle A from rotor axis !9 may be determined in thesame Way:

Distance from 19 to 27 If weight 25 is to move in the manner necessaryto achieve its objective as previously outlined the above two distan esmust be equal. E na-ting the right hand sides of Equations 1 and 2,multiplying both by the common denominator and subtracting identicalterms from the two sides of the equation, we have:

Bg-l-Wa=Bg.cos A +Wa.cos A+ Wb.cos A (3) Distance from 19 to 27h Wb.cosA (Bg+Wa) (l-cos A) (4) b=(a+ secA 1) 5 b= a+% exsec A i (6) ThisEquation 6 indicates that the objectives previously outlined will beattained if the weight is constrained to so move that, as the blade isrocked upward from the horizontal to any flapping angle A above thehorizontal, the weight Will move outward along the blade axis by adistance equal to the external secant of the angle A multiplied by thesum of the distance the weight originally stood from the flapping hingewhen the blade was horizontal and the distance of the center of gravityof the blade proper from the flapping hinge increased in the ratio thatthe mass of the blade proper bears to themass of the weight 25. It willbe noted that if the mass of the weight is decreased relative to that ofthe blade the required stroke of the weight is mass and stroke of theweight it is desirable in actual practice to limit the flapping .angleto not in excess of 15 or thereabouts. An average coning angle ofapproximately half this value is quite usual, so that by taking steps tominimize the departures therefrom the maximum flapping angle may be heldwell below 15. The minimizing of departures from average coning anglemay be effected, without adversely affecting the desirablecharacteristics of the articulated rotor, by attaching each pitchcontrol rod (rod 30 of Figure 12) at a distance well outboard of theflapping hinge 24, and connecting it by a relatively short connectingarm (arm 3! of Figure 5) to the blade spar so that changes from theflapping angle for which the pitch control rod is set will producerelatively great changes in blade pitch. With the maximum blade flappingangles thus limited the mass of weight 25 may be held as low as 20% or25% of that of the blade proper without involving excessive stroke ofthe weight.

In 'theembodiment of the invention illustrated in Figures 5 to '11,inclusive, and as particularly shown in Figures 5 and '6, each blade l lcomprises a skin or covering 34 integrally mounted on ribs 35, which inturnare integrallyattached to a tubular blade spar 3'5, which sparterminates inwardly in a bearing retainer 31 containing a ball thrustbearing 31a co-aiiial with the spar. This bearing serves toattachtheblade to a con necting :link 38 in a manner permittingtheiblade to *be rotated about the spar axis relative to the link 38, tochange "the pitch setting of the blade. Connecting link 38 is in turnattached by means of a flapping hinge 24 .toa lug 39 integral with a hubmember 40. Asshown in Eigure 5, this par ticular embodiment comprises athree-bladed rotor, and there :are therefore two other lugs .38 integralwith this same hub member 4.0 in addition to the one to which the bladeillustratedis attached. Hub member 46 is 'in turn pivotally mounted ona'lrotor drive shaft d1 by means of roller bearings -42 and 43, and isprevented from .maving upwardly :on shaft =41 by a thrust bearing 44which seats again-st a cap integral with the shaft M.

As also illustrated in Figure 5, cap A5 is provided-with three arms 46,each of which =carries a pin .41 to which is pivotally attached ayieldable .linkAB, the other end of which is pivotally attached to -apin 49 mounted in one of the lugs .39 of the hub member 4!]. Cap isillustrated as having three arms 46, and pins are shown for mountingthree links 58, it being assumed that the particular embodimentillustrated is equipped with three such links. However one such link orany other number of such links would serve the purpose, for the linksare provided for transmitting-the drive from the shaft 41 to the hubmember 40 (seeFigure 6) pin a manner which will smooth outirregularities in the drive and will permit the hub to readjust itselfangulanly on the shaft MQ The assembly constitutes a master-drag hinge,whereby any irregular forces which tend to make .a blade advance or lagabout its individual drag hinge in the prior art "constructions can doso, .at least in some degree, .in my present construction, thedifference being that with my arrangement all other blades are forced tosimultaneously advance or lag by the same amount, and displacement ofthe center of gravity of the rotor is avoided. I

The construction of a typical link 43 :is illustrated Figure 9. It isessentially an hydraulic shock absorber equipped with centralizingsprings. It includes .a piston-rod 5!! provided at one end with a hole.51 for pivotal mounting .on the ,pin 41 and provided at theother endwith a piston .52 reciprocably mounted in a closed cylinder 53 filledwith hydraulic fluid. .The piston 52 has a slight amount of clearancebetween it and the cylinder 53 to permit the hydraulic fluid to passfrom one side of the piston to the other at a rate sufficiently slow toavoid rapidreciprocation of I the piston in the cylinder. Mounted in thecylinder between the piston -52 and one head of the cylinder is a spring5 3, while another spring is located between the piston and the oppositecylinder head. The spring 54 is considerably'longer than the spring 55as it is the spring that is compressed by the normal driving of therotor, spring 55 only acting to cushionthe return of the piston to itsnormal position. Integrally attached to the cylinder 53 is an arm 56provided with a hole 51 for pivotally mounting on the pin Ill) 49.Movement of the piston '52 in Ethe cylinder 53 changes the effectivelength of the lllllk from hole 5l to hole 5?, thus changing therotational position of the rotor hub relative to its driving shaft il.The springs E i andbfi yieldablytresist such changes, and the hydraulicfluid in the cylinder limits the rate of such changes.

In the prior artconstr-uction displacement :of any blade aboutitsindividualdrag hingeyunless accompanied by identical displacement ofthe other blades, altered the location of the center of gravity of therotor :and because of the upward slant of the blade altered theeffective tilt of the rotor. These alterations in center of gravitylocation and tilt might -be desired alterations required for properoperation of the craft of prior art types or they might be unwantedalterations introduced by disturbances or irregular ities o'f =one kindor another and might very adversely affect the smooth operation of thecraft. Therefore, in the prior art construction the use of means forcentralizing the blades on their individual drag hinges or retardingtheir movement about such hinges had to be provided verycaut'iously andwere never very satisfactory,

for the centralizing means always prevented the desired displacementsreaching their full proper values, while the retarding means; if any,tended to cause the undesired displacements to persist long enough toproduce very adverse effects and to unduly delay the proper readjustmentof 'de-- sired displacements. However, in my arrangement thedisplacement of the blades about their common drag hinge does notproduce any change in the location of the center of gravity of the rotoror any change in its effective tilt, and therefore the centralizing andretarding means does 'not produce any of the adverse effects abovementioned. Therefore, the amount of centralizing and retarding action isdesigned to give the maximum of rotational smoothness to blade movementwithout having "tobe concerned with other effects, as in the prior art.In the particular embodiment illustrated in Figures 5 to 11, theadjustable weight 25 previously described is provided, not in one piece,but consists of a plurality of pieces comprising primarily two rods 60reciprocable in two cylindersfi l integrally mounted in the ribs 35 ofeach blade 1-1 (see Figure 5). These rods are designed to bereciproca'ted in their cylinders by hydraulic fluid introduced into theouter end of each cylinder, which is the right hand end thereof asviewed in the drawings. Preferably each rod is provided near its outerend with an hydraulic seal and is :constructed with sufficient clearancein the cylinder over the remainder of its length so that slight flexingof the cylinder will not cause binding.

The hydraulic fluid for producing the properli controlled reciprocationof the rods Bil is introduced into the outer ends of the respectivecylinders 61 through tubing 62 by a reciprocab'lehydraulic pump locatedin the blade spar 36 and operated by the flapping movement of the-blade. As shown particularly in Figures 6 and? this hy-' draulic pumpis preferably a multiple cylinder pump comprising a plurality of pistons.64 .(four such pistons vbeing assumed in the particular showingillustrated), each piston acting in a separate cylinder 65, but allcylinders preferably being assembled together into one cylindrical unitand all pistons assembled together into a unit.

The construction of one of these cylinders is illustrated in greaterdetail in Figure 11. In

tegral with the inward end of each cylinder 65 is a cylinder head 66,which is provided with a hole for the piston rod 6? of the correspondingpiston 64 and to which is screwed the outer end of the cylinder 65located next further in toward the rotor hub. Each piston 54, except theouter most one, is provided with a blind tapped hole into which isscrewed the end of the piston rod 6'! of the piston located next furtherout. The space to the left of each piston 64 is filled with hydraulicfluid and communicates with the corresponding portion of the tubing 62,while the space to the right of each piston is empty being connected tothe atmosphere through bleed-hole B8. In the outermost cylinder thebleed-hole may be dispensed with and the entire outer end of thecylinder left open instead.

As will be apparent from Figures 5, 6, and 7, two of the cylinders 65 ofthe pump are preferably connected to one of the cylinders 6! through oneset of tubing 62, and the other two to the other cylinder 6| through aseparate set of tubing 62. The feeding of equal amounts of hydraulicfluid to each of the cylinders 6| may thus be assured.

The entire cylindrical assembly consisting of the plurality of cylinders35 integrally assembled together, and the plurality of pistons 66 andthe piston rods 61 integrally assembled to each other and reciprocablein cylinders 65, is concentrically mounted in blade spar 36, asindicated in Figures 6 and '7, and as will be especially clear fromFigure 8, which shows a cross-section of the blade and particularlyillustrates the position within the blade at which the cylinders 6| maybe located, as well as the location of blade spar 36 and the hydraulicpump mechanism within it. Obviously the number of rods 6 andcorresponding cylinders 6!, as well as the number of pistons 6% andcylinders 65 in the pump unit can be any number from one each up to anynumber of each that may prove desirable.

Means are provided for actuating the pump to feed or permit discharge offluid from the cylinders as the flapping angle of the blade changes. Theinnermost or leftmost piston rod 61 (Figures 6 and 7) is pivotallyattached by means of a pin 10 to a short link H, which in turn ispivotally attached to the upper end of a lever 12. Lever T2, in turn, ispivotall mounted on a pin 13, which is carried by the blade root link38, ex-

tending between two arms 14 which extend downwardly from that link. Atits lower end link 72 carries a roller 15, which roller is preferablyconstructed as a double roller or pair of co-axial rollers integral witheach other, one located immediately adjacent each face of lever 72. Solong as the rotor is in operation roller 15 will be held in firm contactwith lug 76 by the centrifugal force acting on the piston assemblyattached to the upper end of lever 72 and more especially by thecentrifugal force on rods 60 which increases the pressure on thehydraulic fluid which tends to force pistons 64 outward. Roller 75 isdesigned to bear upon the face of a lug 16 which extends integrallyoutward from hub member 40. As the blade, during rotation of the rotor,rocks upwardly from the position in which it is shown in Figure 6 to theposition in which it is shown in Figure 7, the pin 73 moves upwardly andaway from the lug I6 permitting the roller 15 to move upwardly along theface of lug l5. This face is so shaped as to constitute a variable-ratecam having a flatter effective cam slope in that portion of the camcontacted by the cam follower when theblade extends at approximatelyright angles to the rotor axis than in that portion of the cam which iscontacted by the cam follower when the blade has been rocked about itsflapping hinge so as to extend upwardly at an acute angle to said axis,for the first part of this upward rocking permits lever 12 to rockslightl clockwise relative to link 38 while further upward rocking of thblade permits such clockwise rocking at an increasing rate, these ratesall being such that the consequent outward movement of piston rod 51relative to cylinders 55 will be proportional to the value of b in thepreviously developed formula:

b- B A a+ g) exsec (6) wherein A as previously noted is the flappingangle of the blade measured upwardly from the horizontal.

It will be noted that in the above described arrangement the rods 50,which were previously mentioned as primarily constituting the weight 25which is longitudinally adjustable relative to the blade, are not theonly parts carried by the blade which move relative to it as it flaps.The piston rod assembly including pistons (i l and rods 51 so moves, butin my preferred embodiment the movement of this assembly would be only aminor fraction of that of the rods til, but it would be exactlyproportional to and in the same direction as that of these rods. Link 72and the connecting pins would move by substantially the same amount asthe piston assembly while the center of gravity of lever 12 would move ba small fraction of this amount. For instance the movement of the pistonassembly and of link H and the connecting pins may, in a typicalinstance, be A; that of rods 69, while the movement of the center ofgravity of lever 12 (including roller 75) may be that of rods 50. Insuch an instance the mass W of the weight 25 may be considered as madeup of the mass of rods [ill plus 4 that of the piston assembly and oflink H and the connecting pins plus that of lever Weight 25 of thediagrammatic disclosures is really made up, in this embodiment of theweighted sum of all the parts that move longitudinally of the blade asthe blade flaps, and the proper amount of movement for rods 66 can becalculated as b in Equation 6, above, by using as the value for W inthat equation the composite value of the mass arrived at in the mannerabove outlined. The proper piston stroke for each value of the flappingangle A would then, in the particular numerical example above suggested,be 0.252), while the movement of the center of gravity of lever 72 wouldbe 0.1%.

The pressure which roller 15 exerts against lug 76 produces a clockwisemoment on hub member 40 about hinge pin 24. This is the momentdesignated as M1 for one blade and M2 for the other blade in Figure 3.From Figures 6 and 7 it will be evident that, as the blade rocksupwardly, the.

amount of this moment will increase both because the consequent outwardmovements of rods 60 and piston assembly 64, 57 increase the centrifugalforce they exert, and more especially because the direction of thepressure exerted on surface 16 by roller 75 changes so that for thehigher blade positions the line of action of this pressure passesdistinctly further from hinge pin 24, thus correspondingly increasingthe moment set up by this pressure. The consequence is that, aspreviously mentioned, the resulting moment assures 21 increases morerapidly than the corresponding increase in blade napping angle.

previously indicated .if the construction is such that the various partswhich constitute weight 125 are reciprocated inzsuch 1a manner as toaccord with the requirements 10f Equation 6 above, changes in theflapping angle of a blade will not disturb the balance of the :rotor.Therefore the care which has heretofore been exercised in *endeavorlingto secure exact aerodynamic similarity between the various blades willno longer be required for the operation will not now be adverselyaffected it due to .a .difierence in blade lift, one blade tracks higherfor lower than the others, .nor there be any ill effect if :one bladedevelops more :drag than the others, .for no drag displacement of :sucha blade relative to the "others can now resu'lt.

Also the new arrangement eliminates all need for the extreme care whichhas been heretofore exercised to secure and maintain exact mass balanceand similarity in the construction of the various blades :Such care hasbeen exercised in the past because mass iunbalancestoo small to beserious themselves were in danger of becoming the incipient cause ofblade "displacements which might gradually develop under certaincircumstances to troublesome proportions. Since relative dragdisplacements :of the blades are now prevented, and flappingdisplacements counterbalanced, :slight inequalities in mass balance -ordistribution no longer cause the difficulty that they formerly did.Therefore, many types of blade construction which in the past would havebeen considered desirable except for the difiicu'lties which theypresent in regard to the control of mass balance and distribution, andairfoil shape, can now freely be :employed. However some \of these mayinvolve reater mass differences between :the blades than can betolerated even though the effect :on blade displacements is no longer ofconsequence. Therefore I have pro vided means 'for seasily efiectingmass balance of the rotor. Each blade is equipped with two such meanseither 10118 "or both of which may be employed for efiectin the desiredbalance in any given instance.

One of these mcans'for effectingmass balance of the 'rotorcomprisesanzeccentrically adjustable connectionwbetween clink lil :andlever 12. means :is shown in greatest detail Figure 10. As there :shownalboltaflil extends through coaxial holes in the two leftwardlyextending :arms :81 :of the link H. A shouldered portion "82 of thisbelt fits freely into :one of these holes, while a plain sleeve 83slipped over the bolt its :in :the :other. Slipped over the bolt betweenthe shoulder 82 and :sleeve 83 is a flat washer '8] and also aneccentric :sleeve 84 carrying integrally with "it an hexagonal flange:85. Screening down .a nut 86 2;

firmly clamps the-sleeves 8B ,and '84 the lever 12 and the washer -81against the shoulder .82 so that they cannot beirotated relative to eachother. By loosening the :nut86 thehexagonal flange may he rotated tobring the eccentric sleeve 84 into :any desired angular position,following which itmay'be locked in thatposition by tightening the nut.The outer diameter of the eccentric portion :of sleeve [84 this freelyinto a .hole in the top portion of lever 12, :and the length of thiseccentric portion is slightly sless than. the thickness of lever 12 toinsure that the eccentric sleeve M 'willzbe clamped infixed relation tothelever'when the nut 86 is screwed down. "The pivotal connection :oflever 12 to H us established by This 4 22 virtue of the fact thatshoulder 82 and sleeve 83 are always free "to turn in their mating holesin arms 8L It will :be observed (that this pivotal connection is alwayscoaxial with bolt :80 and maybe adjusted relative to the lever byrotation of the eccentric sleeve 84 By reference tolligure 6 or 7 itwill be evident that, if with the blade at any given flapping angle, theeccentric connection :between link H and lever =72 be re-adjusted thepiston rod "Bl-can be moved further into the cylinders '65 or broughtfurther out without disturbing the positionof lever :12 orxthe point ofcontact of roller 1:5 with lug 15. Any such movement of piston :rod 6:?will, of course, result in "a corresponding and greater-movement of bothrods T60, thereby increasing or decreasing the centrifugal force whichthe blade exerts under any given conditions. .=By thus adjusting one ormore of the blades the rotor may be brought to perfect rotationalbalance. This may most easily hedone on a test fixture after assembly ofthe rotor and before mounting it on the craft, the location'(thatischoiceof blade to be readjusted), direction, and approximate.amount of the adjustments to be made :being determined by rotatingtherotor.

The second means provided for .effectingusimilar adjustment :of :massbalance is shown in Figure :5. It includes two cylinders 19d, oneconnected through one tubing system :62 to one cylinder 16L, :and theother similarly connected to the other cylinder 6!. A screw member 91 isprovidediin connection. with each cylinder .90, and it may be screwedany desired amount into "the cylinder and locked :by 'inut 192 The innerend of screw member 9l preferably terminates in an hydraulic-sealer inso close a :fit into 'theLmating portion of cylinder -99 as toeffectively prevent leakage. Thus any inward adjustment of .screw 9|displaces a certain amount of hydraulic fluidwhich through tubin 62causes an equal amount to flow into the respective cylinder 6| andcorrespondingly displaces rod fill.

This arrangement has an advantage :over the previously described meansin that the :two rods.

within each blademay 'be adjusted independently of each other to-shiftthe center of gravity toward oraway from the leadingedge of the blade.Also the eccentric arrangement previously described, when "used alone,has the disadvantage for the purpose above outlined that the'rightwardor leftward adjustment of the pivoted connection of lever 12 to link His ordinarily also necessarily accompanied with 'an upward or downwardadjustment thereof, thereby slightly alterin the efieotive length oflever 'l-Zwhich alteration might prove slightly undesirable undercertain circumstances, and no such disadvantage is connected with the:use of adjustingscrews =9! When, as illustrated, 'both adjusting meansare provided, a still further advantage :may be aseoured from theeccentric adjustment, however, by reference to Equation 6 developedhereinbefore it will be evident that if due to any irregularities inconstruction the ratio of blade weight to counterbalancing weight, orthe distance of blade center of gravity from the flapping hinge differat all from the design values, the amount of stroke of the weight foreach change in flapping angle should be correspondingly increased ordecreased. Therefore if the blades are constructed, :as previouslysuggested, without accurate control over the amount and distribution ofmass therein it is desirable to have the blade counteitbalancingmechanisms equipped with ready means for adjusting the amount of strokeof plungers 60 for any given change in flapping angle; By weighing eachblade and measuring the location of its center of gravity, in the mannerwell known in the art, the proper length of lever I2 can be computed forproducing exactly the proper stroke of plungers to for that particularblade, whereupon the eccentric connection between the lever is and linkII related to that blade can be adjusted and permanently locked to givethis computed effective length of lever. The fact that this verticaladjustment of the connection may also adjust it horizontally causes nodifficulty, for screw members 9! may thereafter be adjusted in themanner previously outlined to correct for this difference along with allother factors affecting rotational balance of the rotor, in a singleoperation.

In order to prevent the droop of the blades, which as previouslymentioned is characteristic of prior art rotors, particularly those ofthe articulated type, I prefer to mount beneath each flapping hinge aspring 95 (see Figures 6 and 7) seated in a socket in hub member ill andengaging, at least when the blade is in the lower part of its range offlapping angles, a crosspiece 96 integral with the blade root link 38.This spring may, if desired, be made only strong enough to raise theblade when it is moving so slowly that its weight becomes of moreconsequence than the aerodynamic and centrifugal forces acting on it.Under such an arrangement the spring would exert a negligible effect ascompared with the large aerodynamic and centrifugal forces acting on theblade during flight, but with a stationary or slowly rotating rotor, atwhich time the droop of the blades is now effective and causes thedangers and difiiculties previously mentioned, the spring is effectiveto rock the blades upward about their flapping hinges, thus eliminatingthe droop and entirely avoiding the disadvantages associated with it.

Alternatively the springs 95 may be made considerably stronger thanabove mentioned, and arranged to be effective over the major portion ofthe range of flapping angles of the blades. In

such a case they may serve the purpose of aug-' menting the moment setup by the pressure of roller I5 against lug '56. As previously notedthis is an unstable moment and increases with increase of blade flappingangle at a rate in excess of the rate of increase of the flapping angle.The moment exerted by spring 95 on the other hand is a stable moment anddecreases with increase of flapping angle, thus tending to offset theincrease in the other moment. As previously noted the moment set up byroller '55 tends to lower the effective point of application of theresultant rotor force on the craft from a prior art position such asindicated by point 32, Figure 3, to a position such as indicated bypoint 33. If in any particular design this particular point ofapplication is considered too low the methods available for raising itinclude, in addition to inward movement of the effective center ofgravity of weight 25 and/or outward spread of drag hinges 24., theincreasing of the moment exerted by spring 95 or more especially theincreasing of the rate at which the moment exerted by it falls oif withincrease of blade angle, for the greater the rate at which the momentset up by spring 95 thus decreases, the less the net increase of thetotal moment effective between the blade and the hub, and consequentlythe less the shift of the resultant rotor force from its prior artlocation. The designer is thus provided with novel means for bringingthe rolling and pitching controls to the exact degree of sensitivenessdesired for any particular craft.

Figure 12 illustrates an embodiment differing in certain respects fromthat disclosed in Figures 5 to 11, inclusive, the principal differencesbeing in connection with the method of mounting, driving, and providingrotational yield in connection with the rotation of the hub member. Theprincipal objects of this alternative arrangement are to provide agreater spread between the flapping hinges and to increase the rotorcontrolling efiect and craft stability. To this end hub member Ella,though similar in construction to the hub member 4 of first embodimentis much larger in diameter. Then instead of providing a driving shaft ofcorrespondingly enlarged diameter, the hub member 40a is mounted bymeans of roller bearings 42a and 43a, generally corresponding to thosesimilarly numbered in the first embodiment, for rotation about a fixedcylindrical frame member IOU having fixed thereto or integral therewitha cap II to which the upward thrust of hub member 46a is transmittedthrough thrust bearings 44a. The drive for the rotor comes from engineshaft I03 through a conventional hydraulic coupling or fluid clutch lill to transmission shaft Hi5, mounted in flanges I E16 and I ill integralwith frame member Iilfi. Integral with shaft I95 near its upper end is agear I98 which meshes with an idler Hill, which idler is also mounted inflanges I as and Iil'l. Idler we in turn meshes with teeth IE8 cut intothe inner face of hub member. 46a. Hub member dila is thus rotated uponthe fixed cylindrical member Ifiil. The effect of a master drag hinge issecured since the hydraulic coupling 5 3 offers little resistance tominor angular readjustments between the engine and the rotor whethersuch readjustments are required to smooth out irregularities in thedriving move ment transmitted by the engineor to permit the blades torespond in limited degree to irregular air conditions encountered.

Figure 12 also illustrates more fully than the preceding figures how thepitch of the blades, Which are supported just as in the firstembodiment, may be controlled both cyclically and simultaneously, and itis to be understood that generally similar pitch control mechanism maybe employed in connection with the first embodiment. A sleeve H2 ismounted for vertical re- 5. ciproeation on the cylindrical frame memberI00.

This sleeve is raised or lowered to secure general increase or decreasein the pitch of all blades. This may be effected, for instance by a forkII3 engaging pins H4 and II 5 which extend outwardly through sleeve H2and serve to pivotally mount a ring H5 inside member I0 3. Ring H6 isconnected to a floating ring 5 I8 by two diametrically opposite linksH9, one of which is shown (partly broken away) in Figure 12. Pin H5 isfixed to or integral with the ring H6 and with an arm I259 which carriesa pin I2! extending through a vertical slot of a Scotch yoke I22 whichmay be reciprocated perpendicularly to the plane of the drawing to rockthe ring II6 on its pins I If and I I5 and to thereby similarly rockfloating ring lit for the exercising of cyclic control.

For exerting cyclic control at right angles to that exerted through ringI I 6 another ring I25 is provided also pivotally mounted on sleeve II2(by means of a pin I'26 and another co-axial pin not shown). An arm I21integral with pin I26 and ring I25 carries a pin I28 which is seated ina vertical slot I29 of a Scotch yoke I30 which may be reciprocated tothe right or left to rock ring I25 on its pivot pins IZ'B, which throughthe two opposite links I3I serves to similarly rock floating ring IIB.Integral with ring H 8 outside of member Illll is ring I33 which througha ball and thrust bearing connection is held in a relation to ring I34which remains at all times fixed except for relativerotati'on of the tworings, ring I34 rotating with the rotor while ring F33 does not rotate.Integral with ring I34 are a plurality of arms I35 (one for each blade),each such arm being universally connectedto vertical link 30 which isconnected to the blade through arm 3| (Figure 5) as previouslydescribed".

It will be evident from the foregoing that when sleeve H2 is raised allfour rods H9 and I=3,I are raised equally, raising rings I'I8, I33 andI34- parallel to themselves, causing equal increases inpitch of allblades. However if either of the" Scotch yokes I22 or I3!) isreadjusted; eitherthe ring H6 or the ring I-2-5 will be tiltedand acorresponding tilting movement will. be transmitted to rings IIB, I33;and I34 causing links '33 to be raised: at one portion of the circuitfor all blades and correspondingly lowered at the opposite portion, thusintroducing cyclic changes of blade pitch.

I claim:

1. In a rotary wing aircraft rotor having, a hub and a blade hinged tosaid hub; the combination of acylinder carried by said blade, a piston.con.- stituting a weight element movable. longitudinally ofthe bladewithin said cylinder; said piston be ing; urged. outwardly with respect.to said hub. in response to centrifugal forces effective during rotationof said rotor, and means comprising a hydraulic pump connected to saidcylinder and actuated by downward hinging movement of said blade withrespect to said hub for controlling the extent of such outward pistonmovement and for actuating said piston to cause movement thereof in adirection toward said hub.

2. In a rotary wing aircraft rotor having a hub and a blade hinged tosaid hub; the combination of a plurality of cylinders carried by saidblade, a piston movable longitudinally of the blade within each of saidcylinders; said pistons collectively constituting a balancing weightcarried by said blade and being urged outwardly with respect to said hubin response to centrifugal forces effective during rotation of saidrotor, and means comprising a plurality of hydraulic pumps each of whichis connected to one of said cylinders and actuated by downward hingingmovement of said blade with respect to said hub for controlling theextent of such outward piston movement and for moving said pistonstoward said hub.

3. In a rotary wing aircraft rotor having a hub and a blade hinged tosaid hub; the combination of a plurality of cylinders carried by saidblade, a piston movable longitudinally of the blade within each of saidcylinders; said pistons collectively constituting a balancing weightcarried by said blade and being urged outwardly with respect to said hubin response to centrifugal forces effective during rotation of saidrotor, and means comprising a plurality of hydraulic pumps havingpumping pistons the area of which substantially exceeds the area of therespective weight pistons and each of which is connected to one of said26 cylinders and actuated by downward hinging movement of said bladewith respect to said hub for controlling the extent of such outwardpiston movement and for moving said pistons toward said hub.

fl. In a rotary wing aircraft rotor having a hub and a plurality ofblades each connected to said hub by a flapping hinge constraining theblade to move relative to the hub in a single plane fixed relative tothe hub; the combination of driving means for said hub comprising aprime mover and a yieldable driving connection between said prime moverand said hub, a plurality of balancing weights each carried by arespective one of said blades and each adjustable longitudinally of itsrespective blade, and means related to each respective blade andautomatically responsive to h-inging displacement of said blade withrespect to said hub for directionally and quantitatively adjusting saidbalancing weight.

5. A bladed rotor for rotary wing aircraft comprising a balancing weightadjustable with respect to the axis of rotation of said rotor, meansincluding a lever having a first operating connection from a blade ofsaid rotor and a second operating connection to said balancing weight;said means being automatically responsive to movement tending todisplace the center of gravity of the rotor transmitted from said bladethrough said first operating connection, for directionally andquantitatively adjusting said balancing weight; and means'for varyingthe effec tive length of said lever to vary the magnitude ofdisplacement of said weight through said second. operating connectioneifected. in response to a given amount of movement of a blade asaforesaid, in combination with separate means for altering the positionof said. balancing weight which corresponds to each given position ofsaid. blade.

6. In a rotary wing aircraft having a hub and a blade hinged to saidhub; the combination of a plurality of separate elements collectivelyconstituting a balancing weight; each of said elements being adjustablewith respect to the axis of rotation of said rotor, and meansautomatically responsive to hinging displacement of said blade withrespect to said hub for directionally and quantitatively adjusting saidelements; said means including a separate device associated with each ofsaid elements for adjusting the associated element in the absence ofhinging displacement of said blade with respect to said hub.

'7. In a rotary wing aircraft rotor having a hub and a blade hinged tosaid hub; the combination of a plurality of separate elementscollectively constituting a balancing weight carried by said blade; eachof said elements being adjustable longitudinally of the blade, meansautomatically responsive to hinging displacement of said blade withrespect to said hub for directionally and quantitatively adjusting saidelements to displace the resultant center of gravity of the blade andsaid elements collectively, and means for separately altering theposition of each of a plurality of said elements longitudinally of theaxis of the blade, in the absence of hinging displacement of the bladewith respect to said hub.

8. In a rotary wing aircraft having a rotatable hub, a blade, and aflapping hinge connecting said blade to said hub; the combination of abalancing weight movable relative to said blade and said hub andradially adjustable with respect to the axis of rotation of said hub, ahydraulic pump having an elem nt directionally and quantita- 27 tivelymovable jointly by said blade and said hub during movement of said bladerelative to said hub upon said flapping hinge, and a connection betweensaid pump and said weight for selectively transmitting movementdirectionally and quantitatively imparted to said pump element to effectrelated directional and quantitative radial adjustment of said weight.

9. A rotary wing aircraft rotor according to claim 8 in which saidbalancing weight is enclosed within said blade and adjustablelongitudinally thereof, and said pump is enclosed within said blade andsaid element of said pump is displaceable longitudinally of the blade.

10. In a rotary wing aircraft having a hub rotatable about a normallyvertical axis, a blade, and a flapping hinge connecting said blade tosaid hub; the combination of a balancing weight carried by said bladeand adjustable longitudb nally of the blade, and means for adjustingsaid weight longitudinally of said blade comprising cooperating cam andcam follower elements, one of said elements being supported by said huband the other by said blade so as to cause the cam follower element tomove along said cam element upon hinging displacement of said blade, anda connection from one of said elements to said weight, the cam elementbeing proportioned to effect a lesser adjustment of said weight per unitof angular displacement of said blade in that portion of the cam elementwhich is contacted by the cam follower element when the blade extends atapproximately right angles to said axis than in that portion of the camelement which is contacted by the cam follower element when the bladehas been rocked about said flapping hinge so as to extend upwardly at anacute angle to said 3X15;

11. In a rotary wing aircraft having a rotatable hub, a blade, and aflapping hinge connecting 28 said blade to said hub; the combination ofa balancing weight enclosed within said blade, carried by said blade andadjustable longitudinally thereof, a mechanism jointly operable by saidblade and said hub during movement of the blade relative to said hubupon said flapping hinge, said mechanism comprising a variable-rate camand a cam follower, and a connection between said mechanism and saidweight for transmitting movement imparted to said mechanism to efiectradial adjustment of said weight.

12. In a rotary wing aircraft having a rotatable hub, a blade, and aflapping hinge connecting said blade to said hub; the combination of abalancing weight enclosed within said blade and adjustablelongitudinally thereof, a lever pivotally mounted on said blade andcooperating with a cam surface on said hub whereby said lever is jointlyoperable by said blade and said hub during movement of the bladerelative to said hub upon said flapping hinge, and a connection betweensaid lever and said Weight for transmitting movement imparted to saidlever to efiect radial adjustment of said weight.

HAROLD T'. AVERY.

REFERENCES CITED The following references are of record in the file ofthis patent:

Stalker Aug. 12,

